Injection molding is a commonly used and versatile process for molding many materials including thermoplastics and thermosets into diverse shapes. Recent injection molding machines utilize a rotary reciprocating screw or auger. As material is introduced into an injection cavity of a barrel by rotation of the screw, pressure builds up inside the injection cavity causing the screw, while rotating, to move away from the mold. When a desired amount of material is in the injection cavity, the rotation of the screw is stopped, and a hydraulic cylinder is activated to push the screw toward the mold; so that the screw functions as a ram forcing material into the mold. In this assembly, a first hydraulic cylinder is used to push the screw forward to inject the material, and a second cylinder is used to hold the barrel in engagement with the mold. Significantly, both of the first and second cylinders are independent of the other components of the injection molding machine and of each other. Further, the cylinders operate indirectly on the components, such as the screw, of the injection molding machine. Therefore, the injection molding machines are undesirably complex having numerous components leading to higher cost, reduced efficiency, reduced reliability, and increased maintenance.
To obtain the highest quality injection molded parts, it is important to control the temperature and density of the material, the pressure in the injection cavity, and the flow rate of the material out of the injection cavity into the mold. Unfortunately, control of these parameters has been limited. Specifically, the indirect relationship between the independent cylinders and the screw precludes high tolerance control of these parameters thereby limiting the quality and consistency of injection molded parts.
Thus, reduction in the complexity of injection molding machines is desirable to reduce the number of parts used in injection molding machines thereby simplifying and reducing the cost of injection molding machines, increasing the reliability and efficiency of injection molding machines, and reducing maintenance on injection molding machines. It is also desirable to more closely control the parameters of mold material temperature, density, pressure, and flow rate to enhance the quality and consistency of injection molded parts. It is further desirable to substantially reduce the time required to change an injection mold and set a machine for a different part size thereby reducing the need for additional injection molding machines and the cost of producing injection molded parts.